1. Field of the Invention
The present invention relates to a length-variable shock absorbing apparatus for a vehicle, and more particularly, to a length-variable shock absorbing apparatus for a vehicle capable of lengthening the length of a bumper in a longitudinal direction of a vehicle to form a space for absorbing collision energy upon collision of the vehicle to secure safety of a driver when a vehicle speed is more that a predetermined level, and reducing the length of the bumper in the longitudinal direction of the vehicle to readily park the vehicle when the vehicle speed is lower than the predetermined level, and a vehicle employing the same.
2. Description of the Related Art
In the recent automobile industries, safety regulations for protection of drivers from collisions of vehicles have been further strengthened. There are laws related to automobile safety standards, and the standards have become stricter with development of automobile technologies. Automobile makers are establishing stricter internal standards to compete with other makers, independently from the laws.
Such automobile safety apparatus may be generally classified into equipment for preventing occurrence of accidents themselves and equipment for protecting drivers in the case of accidents.
In recent times, most automobiles are equipped with electronic control devices for preventing traffic accidents. While the prevention of accidents is the best way of protecting drivers, it is impossible for such apparatus to completely prevent accidents. In addition, such apparatus cannot protect the drivers in the case of accidents. For this reason, various equipment of reducing injury to drivers have been developed.
Impulse is change in momentum, and is in proportion to a time interval over which a force is applied. Therefore, when the same impulse is applied, a magnitude of a force is in reverse proportion to a time interval over which the force is applied. That is, if a vehicle collides at a high speed, since change in momentum is large, the magnitude of the force applied to a passenger increases. Therefore, when a vehicle is designed such that a deformation section of the vehicle becomes longer when the vehicle collides at a high speed, the length of a collision energy absorbing section may increase to relatively reduce the force applied to the passenger. On the other hand, since impulse is small when a vehicle collides at a low speed, the length of the collision energy absorbing section may be reduced to consider both driving performance and parking convenience.
For example, safety belts, airbags, etc., can protect drivers when vehicles collide. These equipment functions to increase a time interval over which a shock is absorbed to instantly reduce the force applied to the passenger. However, in the case of a small-sized vehicle having a relatively short length, even when the vehicle is provided with the equipment, it is difficult for the vehicle to substantially reduce impulse due to its structural disadvantages as compared with a mid-or large-sized vehicle. In particular, when the small-sized vehicle collides at a high speed, change in acceleration is very large and a time interval for dissipating the colliding energy is insufficient, increasing probability of injury to the passenger.
In order to solve the problems, various researches have been performed to improve the structures of vehicles to effectively absorb collision energy or employ novel energy absorbing materials. In relation to improvement of the vehicle structure, a bumper that can project immediately before collision may be used. However, the bumper may project even when there is no collision, possibly causing traffic accidents. Moreover, a hydraulic or pneumatic bumper is very expensive and heavy.